Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURERS MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-38-40-380-001 Construct Saturation Curve to Determine Correct Peening Parameters

   1. The three factors in the subsequent list dictate how you perform the procedure and the quantity of peening necessary.

      1. Flap rotation speed

      2. Peening time or duration

      3. Mandrel height

   2. It is necessary to construct a saturation curve each time one or more of the changes in the subsequent list occurs:

      1. Change in operator

      2. Change in equipment or in flap rotation speed

      3. A different type or group of parts

   3. Install the Almen Test Strip in a Magnetic Almen Strip Holder. Make sure the indicator pointer pushes against the surface of the test strip that is not being peened.

   4. The Almen Test Strip must be flat in 0.000 +/- 0.001 in. (0.000 +/- 0.025 mm) when measured on an Almen Gage. When you measure the flatness of the specimen, you must make an adjustment for the effect of the gage magnet. Measure the flatness from both faces of the specimen, and then get an average of the results.

   5. Peen the Almen Test Strip as follows:

      1. Install the mandrel in the middle of the Flap Assembly. Lock the mandrel in the chuck of the Flexible Shaft Grinder Series 6-14 (Low Speed).

      2. Use the graph of the intensity/speed curve in Figure to select the initial tool speed.

      3. Set the parallel position of the mandrel and move it in a continuous motion at a distance of 0.100 - 0.125 in. (2.54 - 3.18 mm) the test strip surface. See Figure. If the mandrel is set too high, it will vibrate too much and the tool will bounce.

      4. Set the speed of the flapper to create the correct pressure. Keep the correct pressure as indicated by individual peen marks. Too much pressure will cause the shot metal to drag, which will score the surface and will cause the wheel to break. See Figure.

      5. Peen the Almen Test Strip along its full length for two minutes.

         1. To make sure that peening coverage is the same on all sides, use a circular or oscillating motion over the full area. Use continuous motion while you move the mandrel in rows across the full length of the test strip. Make an overlap of each row. See Figure.

      6. Set the Almen Test Strip on the Almen Gage and measure the height of the curve.

      7. Plot the peening time and the measured arc height on a graph as shown in Figure.

      8. Do the above steps in this procedure to peen the Almen Test Strip on another test strip using the same limits and set points, but increase the peening time by two minutes. Peen additional test strips for different peening times in two-minute increments until you have a sufficient number of points on the graph to make a curve (saturation curve). See Figure.

      9. Use this curve to find the saturation point. The saturation point is the point on the curve at the minimum peening time for which a 100 percent increase in the peening time increases the arc height by no more than 10 percent. See Figure.

      10. Compare the saturation point on the curve to the peening intensity specified in the manual. If the test setup does not give the specified intensity, follow the subsequent steps.

          1. Do a test with a different tool speed (increase the speed to increase the intensity or decrease the speed to decrease the intensity). The curves in Figure show peening time and intensities at different tool speeds. These curves are approximate because results can change when you use manually-controlled equipment.

          2. Run a new group of Almen Test Strips to find a new saturation curve. Compare the new curve with the necessary intensity.

      11. Multiply the saturation time (T in Figure) by 1.25 (125 percent) to get the correct peening time.

2. SUBTASK 70-38-40-380-002 Peen Areas 2 sq in. (1290 sq. mm) or Smaller

   1. When necessary, mask areas of the part not to be peened with either a mechanical mask or sufficient layers of suitable tape, such as CoMat 02-062 MASKING TAPE, CoMat 02-228 MASKING TAPE (HEAVY DUTY), CoMat 02-232 MASKING TAPE, or CoMat 02-369 MASKING TAPE (HEAVY) .

   2. Make sure that the edges of the tape bond tightly to the part.

   3. If area to be peened is flat, position this area in a horizontal plane.

   4. If area is on a curved surface, position with approximate center of area up for maximum access.

   5. Peen designated area with the same parameters (tool speed, time and distance) and procedure that was used to find the saturation curve.

      NOTE

      The operator performing the repair operation must be the same operator who peened the test strips to find the saturation curve.

   6. Examine rotary flap at intervals for missing balls. Replace flap if more than 2 balls are missing from one of the sides.

   7. If you applied maskant, remove it and clean all remaining maskant material from the part by SPM TASK 70-11-26-300-503 solvent wipe method.

3. SUBTASK 70-38-40-380-003 Peen Areas Larger Than 2 sq in. (1290 sq. mm)

   1. Repair area must be divided into sections, less than 2 sq. in. (1290 sq. mm.)

   2. Each section must be completely peened before you continue to the next section.

   3. When necessary, mask areas of the part not to be peened with either a mechanical mask or sufficient layers of suitable tape, such as CoMat 02-062 MASKING TAPE, CoMat 02-228 MASKING TAPE (HEAVY DUTY), CoMat 02-232 MASKING TAPE, or CoMat 02-369 MASKING TAPE (HEAVY).

   4. Make sure that the edges of the tape bond tightly to the part.

   5. If area to be peened is flat, position this area in a horizontal plane.

   6. If area is on a curved surface, position with approximate center of area up for maximum access.

   7. Peen designated area with the same parameters (tool speed, time and distance) and procedure that was used to find the saturation curve.

      NOTE

      The operator performing the repair operation must be the same operator who peened the test strips to find the saturation curve.

   8. Examine rotary flap at intervals for missing balls. Replace flap if more than 2 balls are missing from one of the sides.

   9. You must have overlap at section boundaries.

   10. Prevent a sharp transition from full peening intensity to zero peening intensity. Zones in which peening is optional or zones in which peening is not required to be complete, should exhibit a decreasing density of marks from full peening intensity to zero peening intensity. See Figure.

   11. If you applied maskant, remove it and clean all remaining maskant material from the part by SPM TASK 70-11-26-300-503 solvent wipe method.

4. SUBTASK 70-38-40-380-004 Check for Peening Coverage

   1. Examine the coverage area at 10x magnification.

      1. Coverage must be the same on all surfaces and complete across the full length and width of the strip.

      2. If you see that the area is not fully peened, or if the area does not have the correct overlap, follow the subsequent steps.

         1. Run the Almen Test Strip and compare it to the test strip you used to calculate the saturation curve. If there is a difference, find the cause (change in speed, time, or distance).

         2. Peen the area again to get the correct coverage.

5. SUBTASK 70-38-40-380-005 Corrosion Prevention

   1. Preserve the part as necessary by SPM TASK 70-38-37-300-503.

Figure: Intensity/Time Determination

Intensity/Time Determination



Figure: Effects Of Correct Flap Pressure And Excessive Flap Pressure

Effects Of Correct Flap Pressure And Excessive Flap Pressure



Figure: Mandrel Position

Mandrel Position



Figure: Typical Overlapping - Circular Motion Pattern For Flap Peening

Typical Overlapping - Circular Motion Pattern For Flap Peening



Figure: Peen Intensity/Tool Speed

Peen Intensity/Tool Speed



Figure: Transition From Full Intensity To Zero Intensity

Transition From Full Intensity To Zero Intensity



Figure: Saturation Curve

Saturation Curve